1. Field of the Invention
The present invention relates to a video control apparatus and video control method and, more particularly, to a video control apparatus having a plurality of connection terminals to which external devices for transmitting video and audio data are connected, and a control method thereof.
2. Description of the Related Art
In recent years, in order to receive a high-resolution video signal from an external device such as a hard disk recorder to a television receiver, an interface called HDMI (High-Definition Multimedia Interface) is used.
The HDMI can transmit video and audio data via a single cable, and is advantageously free from any troublesome need to connect a plurality of cables. For this reason, the number of HDMI ports for HDMI connections equipped on a video control apparatus is increasing year by year.
The HDMI performs information transmission between connected devices using a TMDS (Transition Minimized Differential Signaling) channel, CEC (Consumer Electronics Control) channel, and DDC (Display Data Channel). The TMDS channel is used to transmit video data, audio data, and auxiliary data.
The CEC channel is used to transmit device control signals. Using a communication of the CEC channel (to be referred to as a CEC communication hereinafter), a video control apparatus and an external device, which are connected via the HDMI, can be cooperatively controlled from a single remote control in place of their individual remote controls. For example, functions of turning off the power supply of the external device in cooperation with power-OFF of the video control apparatus, and switching the input of the video control apparatus in cooperation with start of playback of the external device can be implemented.
In the HDMI, EDID (Extended Display Identification Data) is transmitted by the DDC, and HDCP (High-bandwidth Digital Content Protection) authentication is performed.
Using the EDID, various kinds of information such as information associated with the video control apparatus and a source physical address (to be referred to as a physical address hereinafter) are transmitted. The physical address indicates the device connected to that HDMI port. That is, using the EDID, external devices can be notified of the resolutions and audio stream information supported by the video control apparatus, the loudspeaker information of the video control apparatus, and the physical address of the video control apparatus to be acquired by the external device.
According to HDCP, video and audio data transmitted from the external device to the video control apparatus are encrypted using a public key method. In HDMI, HDCP authentication is executed by performing communication via an HDMI cable. As a result, for example, when the external device cannot authenticate a video control apparatus, it denies transmission of video and audio data to that video control apparatus.
Japanese Patent Laid-Open No. 2007-78980 describes a technique associated with a DDC communication. The DDC communication initiates when the video control apparatus side switches an HDMI HPD (Hot Plug Detect) signal from OFF to ON. According to Japanese Patent Laid-Open No. 2007-78980, when the formats of video and audio data transmitted from the external device side according to this DDC communication are different from those set on the video control apparatus side, the video control apparatus side switches the HPD signal from OFF to ON again, thus performing the DDC communication again. As a result, an external device can be prevented from being held in a state in which no video and audio data are output in a case where a DDC communication is failure.
A case will be examined below wherein an input switching operation of a video control apparatus is performed using the CEC function in an environment in which a plurality of external devices are connected to one video control apparatus via HDMI. In this case, upon performing the input switching operation by the CEC function, the video control apparatus has to transmit EDID to the respective external devices, and generate physical addresses of the respective external devices in advance. For this purpose, the video control apparatus has to incorporate EDID ROMs, each storing EDID information at respective HDMI ports.
On the other hand, the video control apparatus holds authentication information required for HDCP authentication in an HDCP ROM. This authentication information is required to perform authentication for decrypting encrypted video and audio data transmitted from each external device to the video control apparatus. For this reason, the video control apparatus need only have as many HDCP ROMs as the number of HDMI ports that can be simultaneously displayed on one screen.
That is, the EDID ROMs should be equipped in correspondence with respective HDMI ports, but the number of the HDCP ROMs can be smaller than the number of HDMI ports of the video control apparatus.
In this way, when the number of EDID ROMs is smaller than that of HDCP ROMs, if a DDC communication is made between the external device and the video control apparatus, the external device can access the EDID ROM but it often cannot access the HDCP ROM. In this case, the external device cannot obtain any response to an access request to the HDCP ROM, and the state of a DDC line becomes indefinite. When the video control apparatus makes the input switching operation in an indefinite state of the DDC line, a DDC access does not resume to a normal state, and display of video data and output of audio data may often be disabled.
For example, when the external device selected by the input switching operation cannot access the HDCP ROM and cannot authenticate the video control apparatus by the HDCP, transmission of video and audio data to the external device are denied external device. Also, for example, the external device may often not resume to a normal state from the response waiting state of an access to the HDCP ROM.
In Japanese Patent Laid-Open No. 2007-78980 described above, a receiver monitors video and audio data to be received, and checks if video and audio data in formats supported by the receiver are received. If it is determined that video and audio data in formats which are not supported by the receiver are received, the receiver recognizes the data as abnormal. Upon recognition of reception of the abnormal data, an HPD signal is switched to OFF and is then switched to ON again, thus initiating a DDC access again.
However, according to the technique disclosed in Japanese Patent Laid-Open No. 2007-78980, a circuit that monitors video and audio data is required, thus posing a problem. Also, in Japanese Patent Laid-Open No. 2007-78980, in order to check if received video and audio data are abnormal data, format detection of these received data is required. For this reason, a predetermined period of time is required until it is recognized that the received video and audio data are abnormal data, thus posing another problem.